In the past, processing agents and its process for flammable or combustible fibers and plastics with flame retardancy have been studied.
For example, since polyester fibers have excellent characteristics of mechanical properties and easy processing, they are used in various fields including clothes, interior decorations, padding, nonwoven fabrics, industrial materials and the like. More specifically, polyester fibers are used as materials for interior in hotels, hospitals, movie theaters and the like. However, polyester fibers catch fire easily, and the strict fire laws for the above use are established in order to minimize the accidents caused by matches and tobaccos. Since an awareness of disaster prevention is increased in recent years, polyester fibers having flame retardancy are wished to be developed for safe and comfortable living environment.
Halogen compounds, typically hexabromocyclododecane (HBCD), are mainly used as a flame retardant for polyester fibers. However, these compounds are recently proceeding toward being regulated as persistent and bio-accumulation. Also, since toxic hydrogen halide is generated when flame-retarded products are burnt, flame retardants with a high level of safety are desired. Further, there is a high risk of the above-mentioned halogen compounds to be contaminated in liquid waste of flame retarding substances and could leak with it and it may develop into environmental problems. Therefore, researches for phosphorus compounds not containing halogens as a flame retardant for polyester fibers are actively carried out.
Phosphorus compounds are generally used in various fields as multifunction compounds and different kinds thereof are developed. Particularly, use of the phosphorus compounds as a flame retardant is previously well-known. Also, flame-retardant resins are varied and include thermoplastic resins such as polycarbonate resin, ABS resin, PPE resin, polyester resin or polyester fibers (e.g. polyethyleneterephthalate and polybutyleneterephthalate) and mixed resin thereof; and thermosetting resins such as polyurethane resin, epoxy resin, phenol resin and the like.
Flame retardancy of resins depends on the percentage of phosphorus content in a phosphorus compound mixed as a flame retardant and the flame retardancy is generally higher as the percentage of the phosphorus content increases. However, this generality is not necessarily applied to polyester fibers when flame-retarding the fibers.
Namely, although the polyester fibers are flame-retarded by using as the flame retardant the phosphorus compounds having a high percentage of the phosphorus content, and then if the phosphorus compounds do not get into the inside of the fibers and adhere to a surface of the fibers, the phosphorus compounds are easily fallen off and the flame retardancy cannot be maintained. When the flame-retarded polyester fibers are used for clothes or the like, for example, the phosphorus compounds are easily fallen off from the fibers by washing or laundering. On the other hand, although the polyester fibers are flame-retarded by using as the flame retardant the phosphorus compounds having a low percentage of the phosphorus content, and then if the phosphorus compounds are highly permeable into the fibers and physical adhesiveness of the fibers to the phosphorus compounds is powerful, the flame retardancy can be maintained.
Therefore, from the point of view of providing sufficient flame retardancy to the fibers and reducing the amount of the flame retardants when the polyester fibers are flame-retarded, the phosphorus compounds that are high in phosphorus content, are highly adhesive to the polyester fibers and are not easily desorbed are desirable.
A flame retardant for polyester fibers comprising phosphorus compounds not containing halogens and a method for flame-retarding thereof are, for example, described in the following prior art.
Japanese Unexamined Patent Application No. 2002-275473 (Patent Document 1) discloses phosphorus compounds having a dibenzoxaphosphorine oxide structure. These phosphorus compounds have relatively a high flame retarding property as a phosphorus compound not containing halogens and are highly penetrate into polyester fibers.
However, these phosphorus compounds are a persistent substance which is proceeding toward being regulated. Also, these phosphorus compounds tend to prevent dyes from fixing to the fibers and the dyed fibers with a flame retardant are inferior in lightfastness.
Japanese Unexamined Patent Application No. 2000-328445 (Patent Document 2) and Japanese Unexamined Patent Application No. 2003-27373 (Patent Document 3) disclose resorcinol bis(diphenylphosphate) (RDP) as a phosphorus compound. This RDP has good exhaustion and an adequate flame retarding property.
However, since this RDP has low fastness to rubbing because of liquid and is inferior in resistance to hydrolysis as a characteristic of the compound itself, a dispersing liquid containing the RDP as a flame retardant is inferior in storability; the dyed fibers with the flame retardant are inferior in durability; and use of the RDP is considerably limited because of a low dyeing property.
Japanese Unexamined Patent Application No. HEI 8(1996)-41781 (Patent Document 4) and Japanese Unexamined Patent Application No. 2001-254268 (Patent Document 5) disclose resorcinol bis(di-2,6-xylylphosphate) (product name: PX-200 manufactured by Daihachi Chemical Industry Co., Ltd.) as a phosphorus compound. This phosphorus compound has an excellent flame retarding property to resins.
However, a flame retardant having a better flame retarding property even after washing and laundering tests is further expected for flame-retarding the fibers.
Although ordinary phosphates of a non-halogen type commercially available in a field of thermoplastic resins or the like are used as a flame retardant for polyester fibers, necessary exhaustion or flame retardancy may not be obtained. Even if obtained, the flame retardant cannot practically satisfy the entire conditions such as lack of lightfastness or fastness to rubbing.    Patent Document 1: Japanese Unexamined Patent Application No. 2002-275473    Patent Document 2: Japanese Unexamined Patent Application No. 2000-328445    Patent Document 3: Japanese Unexamined Patent Application No. 2003-27373    Patent Document 4: Japanese Unexamined Patent Application No. HEI 8 (1996)-41781    Patent Document 5: Japanese Unexamined Patent Application No. 2001-254268